There's another brace of high-stakes contest for delegates on tap for Tuesday, and the polls point to momentum shifting again toward Sen. Bernie Sanders in at least two key states.

Democrats are set to hold primaries on Tuesday in Florida, Illinois, Missouri, North Carolina and Ohio, with former Secretary of State Hillary Clinton leading in all five states.

But polls released Sunday for Illinois show a tight race between Sanders and Clinton, with one giving the Vermont senator a slight edge. The NBC News/Wall Street Journal/Marist poll gives Clinton a 51-percent-to-45-percent edge, while the CBSNews/YouGov poll shows Sanders leading 48 percent to 46 percent.

Polls released earlier in March show Clinton with 42- and 37-percentage-point leads in Illinois, where 182 delegates are at stake.

The Sanders campaign is conjuring up the possibility of upset wins on Tuesday, writing to supporters in a fundraising email sent on Saturday, "think about how you felt when we staged the greatest comeback in political history when we won Michigan."

Sanders won last Tuesday in Michigan, where the polls showed Clinton in the lead right up until election day. On election day, FiveThirtyEight forecast Clinton with better than 99 percent chance of winning.

In North Carolina, Clinton holds a 20-point lead in the RealClear Politics average of polls, while in Florida -- Tuesday's biggest prize with 246 delegates -- she leads by nearly 31 points.

In the single poll for Missouri posted on RealClear Politics, released Friday, Clinton is up by 7 percentage points.